Many aircraft have flight control surfaces that are controlled by mechanical actuation systems that are driven by hydraulic power drive units. The aircraft also has other hydraulically powered devices in a separate hydraulic power drive system. A hydraulic power transfer unit is used for transmitting power from one aircraft hydraulic system to another in the event that a pump in one of the hydraulic systems fails.
A mechanical actuation system for a flight control surface, such as a flap, may be in the form of a ballscrew actuator with a drive input derived from a power drive unit of the type disclosed in my prior application, Ser. No. 363,701, filed Mar. 30, 1982. A power drive unit can incorporate a variable displacement axial piston hydraulic displacement device having a rotatable drive shaft that can be connected to a load, such as a ballscrew actuator. Additionally, the power drive unit has a pump as a source of hydraulic power connected to the hydraulic displacement device and with there being suitable controls for setting the displacement of the hydraulic displacement device and the control of hydraulic flow thereto.
It is also known to provide for redundancy in the mechanical actuation system by having a pair of power drive units both connected to the mechanical actuation system in order to assure operation of the flight control surfaces, even though there may be a failure in one of the power drive units. An illustration of such a redundant system is shown in FIG. 1 wherein a pair of variable displacement hydraulic devices of separate power drive units have their drive shafts connected to a speed-summing gear train which may be in the form of a differential and which has an output which is connectable to the mechanical actuation system. It is a characteristic of the speed-summing gear train that the mechanical actuation system can be driven by both of the hydraulic displacement devices or driven by only one of the hydraulic displacement devices when the other is inoperable.
A typical prior art hydraulic power transfer unit for transferring hydraulic power from one hydraulic circuit to another has a pair of hydraulic displacement devices in the separate hydraulic circuits and which are mechanically interconnected, as seen in FIG. 2 of the application drawings. The hydraulic displacement device in one circuit can operate as a motor and, through the mechanical connecting shaft, the other hydraulic displacement device is driven as a pump to transform the mechanical shaft power back into hydraulic power to the hydraulic system having the hydraulic displacement device operating as a pump. It will be evident that this relation between the two hydraulic displacement devices can be reversed in the event that there is a reversal in the hydraulic circuit that has failed.
Other examples of power drive units including control of the displacement of a hydraulic variable displacement axial piston unit are shown in the Flippo Pat. No. 4,191,094 and the Aldrich Pat. No. 4,210,066, owned by the assignee of this application.
Hydraulic power drive units, used either singly or in a redundant combination, for providing a mechanical output and hydraulic power transfer units are known in the prior art; however, there is no known integration of the power drive and power transfer functions into a single unit whereby the hydraulic power drive units are associated with structure whereby they can function to either provide a power drive output or power transfer between hydraulic systems.